Completion of the total synthesis of the gastrointestinal hormone, cholecystokinin. The biological activity of the entire chain of 33 amino acid residues and of shorter chains, e.g. with 17 residues, will be compared. The role of ion-pairs in hormone-receptor interaction and in the stabilization of the preferred conformation found in certain peptide hormones will be studied through the synthesis and examination of analogs of oxytocin and secretin. The synthesis of a secretin analog with reduced effect on the pancreas, but high potency in the inhibition of gastric secretion and of gastric motility, is expected. For improvements in the methodology and techniques of peptide synthesis, a search is planned for new solvents useful in the preparation of long chains.